1. Field of the Invention
The subject invention relates to liquid or fluid pressure transducers, including differential pressure transducers, and to other apparatus and devices, as well as to methods, for providing a signal in response to a force producing physical condition.
2. Description of the Prior Art
In the case of fluid pressure transducers there exists the problem that the transducing devices for generating an electric or other pressure signal, are often attacked or rendered useless by the fluid applied to the transducer. This tendency is particularly strong when the applied fluid is of a corrosive type. This problem is aggravated in the case of differential pressure transducers, where typically two fluids are applied to the transducer. Under those circumstances, and especially in the case of corrosive fluids, emersion of the transducing elements into either fluid will rapidly impair or destroy the transducing function. Some prior-art designs have attempted to solve this problem by providing a separate diaphragm for each fluid emitted to the transducer, and by arranging the transducing elements in the space between the two diaphragms. In those designs, the diaphragms were supposed to shield the transducing elements from the fluids applied to the transducer.
Proposals of the latter type are encumbered by several disadvantages, which includes the fact that an involvement of more than one diaphragm will not only cause significantly higher expenses and bulkier designs, but will also introduce different diaphragm characteristics and similar mechanical and physical problems into the transducing function.
Against this background, two kinds of prior-art proposals for separating the transducing elements from the remainder of the transducer with the aid of bellows or similar flexible tubing can be discerned. In both kinds of proposals, a bellows structure is relatively stationarily mounted at one end and has a free opposite end.
In one kind of these proposals, the bellows structure is designed and arranged for depression of the free end toward the relatively stationary end in an axial or longitudinal direction through the bellows structure. This kind of design may, for instance, be seen from U.S. Pat. Nos. 2,867,115, 2,956,252, 3,020,405, 3,047,022, 3,559,488, 3,660,745, 3,756,085, 3,780,588, and 3,845,348. Application of this principle to a telephone transmitter may be seen from U.S. Pat. No. 2,191,992.
In the other kind of proposal, the free end of the bellows structure is moved laterally of the longitudinal bellows axis as may, for instance, be seen from U.S. Pat. Nos. 3,089,109 and 3,485,104.
In practice, both kinds of proposals are disadvantageous for several reasons, including the fact that the characteristics of the bellows structure with these designs will adversely enter into the transducing function, and the fact that the bellows structure in such designs will be exposed or subjected to axial compression, which will either falsify the transducer output or require special expensive and cumbersome measures for an avoidance or compensation of that deleterious effect.
Another proposal, mentioned here for the sake of completeness, is apparent from U.S. Pat. No. 3,127,571, and provides the transducing elements outside of a flexible tube into which the pressurized fluid is injected. That design is not practically suitable for differential pressure transducer designs and inherently lacks the advantages attainable with a well-defined diaphragm construction.
How little proposals from unrelated fields are able to solve these problems is, for instance, apparent from U.S. Pat. No. 3,695,096 which shows a strain detecting load cell that relies on a shearing stress type of operation which could never be carried out by a fluid pressure actuated diaphragm of a fluid transducer, and from U.S. Pat. No. 3,857,452 which employs a load cell that relies for its operation on the deformation of a heavy bolt-like solid body and is thus similarly deficient for present purposes.